Phospholipase A.sub.2 (PLA.sub.2) is an enzyme which acts on phospholipids existing in cell membrane and hydrolyzes an ester bond at the second position of the phospholipids. There are known two kinds of PLA.sub.2, i.e., membrane-associated PLA.sub.2 and pancreatic PLA.sub.2.
Membrane-associated PLA.sub.2 acts on phospholipids to release arachidonic acid (AA) from the phospholipids. The AA is converted into prostaglandins, thromboxanes and leukotrienes, which are physiologically active substances inducing various inflammatory diseases and allergic diseases.
On the other hand, pancreatic PLA.sub.2 degrades phosphoric acid and destroys cell membrane, thereby to produce lysolecithin having strong cytotoxicity. Recently, much importance has been attached to pancreatitis, severity in pancreatitis and multiple organ failure induced by such destructive activity on cell membrane. Further, it is reported that membrane-associated PLA.sub.2 is also concerned with these diseases.
Accordingly, the inhibition on PLA.sub.2 leads to the suppression of the release of AA, a precursor of various physiologically active substances, and therefore, it is considered to be useful for the prevention and/or the treatment of various inflammatory and allergic diseases. Furthermore, it is considered to be useful for the prevention and/or the treatment of pancreatitis, severity in pancreatitis and multiple organ failure due to the inhibition of destructive activity on cell membrane.